1. Field of the Invention
This invention pertains generally to vacuum interrupters which provide protection in electric power circuits and, more particularly, to vacuum interrupters or vacuum envelopes including end shields that provide a self-alignment function. The invention also pertains to a self-alignment method for ends shields of vacuum interrupters. The invention further pertains to vacuum circuit interrupters including vacuum interrupters having end shields that provide a self-alignment function.
2. Background Information
Vacuum circuit interrupters (e.g., without limitation, vacuum circuit breakers; vacuum switches; load break switches) provide protection for electrical systems from electrical fault conditions such as current overloads, short circuits, and low level voltage conditions. Typically, vacuum circuit interrupters include a spring-powered or other suitable operating mechanism, which opens electrical contacts inside a number of vacuum interrupters to interrupt the current flowing through the conductors in an electrical system in response to abnormal conditions.
Vacuum interrupters include separable main contacts disposed within an insulated and hermetically sealed vacuum chamber. The vacuum chamber typically includes a number of sections of ceramics (e.g., a number of tubular ceramic portions) for electrical insulation capped by a number of end members (e.g., metal components, such as metal end plates; end caps; seal cups) to form an envelope in which a vacuum may be drawn. The ceramic section is typically cylindrical; however, other suitable cross-sectional shapes may be used. Two end members are typically employed. Where there are multiple ceramic sections, an internal center shield is disposed between the ceramic sections.
The main contacts are electrically connected to the external circuit to be protected by the vacuum circuit interrupter by electrode stems, typically an elongated member made from high purity copper. A contact and a stem are identified collectively as an electrode. Generally, one of the contacts is fixed relative to the vacuum chamber as well as to the external circuit. The fixed contact is mounted in the vacuum envelope on a first electrode extending through one end member. The other contact is movable relative to the vacuum envelope. The moveable contact is mounted on a moveable electrode axially slideable through the other end member. The movable contact is driven by the operating mechanism and the motion of the operating mechanism is transferred inside the vacuum envelope by a coupling that includes a sealed metallic bellows. The fixed and moveable contacts form a pair of separable contacts which are opened and closed by movement of the moveable electrode in response to the operating mechanism located outside of the vacuum envelope. The electrodes, end members, bellows, ceramic shell(s), and the internal center shield, if any, are joined together to form a vacuum interrupter capable of maintaining a vacuum at a suitable level for an extended period of time.
When the separable contacts are opened with current flowing through the vacuum interrupter, a metal-vapor arc is struck between the contact surfaces. This arc continues until the current is interrupted, typically as the alternating current goes through a zero crossing. In order to prevent the metal vapor from condensing on the ceramic insulator, several metal vapor shields are typically provided within the vacuum envelope. For example, the metal vapor shields can be between the contacts and the ceramic inside the vacuum envelope, and at one or both ends of the envelope.
During the manufacturing of sub-assemblies, it is known to use an external alignment flange to align the seal cup and end shield. In addition, during the manufacturing of tube assemblies, external self-aligning ceramic fixtures are used to align the seal cup to the ceramic. These, however, can slow furnace run times, reduce productivity, stick to the sub-assembly and/or shield radiant heat from braze joints causing various components to be decoupled.
In the event that the end shield is not properly secured in the vacuum interrupter, then electrical shorts can result.
There is room for improvement in vacuum envelopes and vacuum interrupters employing end shields.
There is also room for improvement in vacuum circuit interrupters, which employ vacuum interrupters including end shields.
There is further room for improvements in methods of aligning end shields of vacuum envelopes and vacuum interrupters.